The long term objective is to identify the genes and gene products that regulate ovary development in the chick embryo and to determine homologies with testis development in mammals. Unlike other organs which have but one fate, the gonadal primordium is biopotential. The W chromosome of chicks is found only in females, but its relationship to ovary development is unclear. It is proposed that a regulatory gene provides the stimulus for gonadal differentiation at a critical period of embryogenesis. The ovary determining factor provides a "head start" to pre-follicle cells which in turn produce growth factors that direct the development of the ovary. There is a labile period when environmental and physiological conditions may act to inhibit growth of the somatic cells of the biopotential gonad, and these cells become Sertoli cells by default, resulting in sex reversal. The hypothesis will be tested by use of immunohistochemistry and tissue culture. Growth factors localized to somatic cells of the biopotential gonad, by in situ hybridization will be scrutinized for their role in ovary development. Sex specific proteins present at the time of ovary morphogenesis will be isolated by 2-dimensional gel electrophoresis and electroelution, and antibodies will be made against them for assay of gene function after production of cDNA libraries. The E chromosome probe will be used throughout the study of identify the genetic sex of embryos. Chick embryos have served for decades as models for organogenesis of warm- blooded vertebrates, and they are particularly useful for student research because they are readily accessible to experimental manipulation. The results will provide basic information that may be extrapolated to sex determination in humans, as well as to morphogenesis of organs whose differentiation has but one normal potential.